Following [1]} and [2]}, we estimate differences in treatment effect on four groups of students, corresponding to whether or not they were invited to participate in the meetings, and also whether or not they had at least one network connection who was invited to participate. Figure REF  shows estimates of \(\mathbb {E}[\tau ^{\text{matched}}]\)  for units that were matched based on school and number of eligible friends. Similar results were found using weighting or matching. A significant difference in effects was found between two groups;
as a result of not inviting the control units to participate, units in control whose friends were also in control were affected more adversely than those who were treated and had at least one treated friend.
